1. Field of the Invention
This invention relates to an absolute position electronic transducer. In particular, the invention relates to an absolute position transducer using one or more transducer elements that output a signal having a position dependent amplitude that varies at two different spatial frequencies.
2. Description of Related Art
Various movement or position transducing systems are currently available. These transducers are able to sense linear, rotary or angular movement.
An inductive absolute position transducer system is disclosed in U.S. Pat. No. 5,841,274 to Masreliez et al., incorporated herein by reference in its entirety. In this inductive absolute position transducer system, the system has two members movable relative to each other and includes a plurality of fine track transducers. Each fine track transducer is associated with a particular spatial wavelength.
Another inductive absolute position transducer system is disclosed in co-pending U.S. patent application Ser. No. 09/213,268, incorporated herein by reference in its entirety. The incorporated 268 application describes a reduced offset absolute position transducer that has at least one magnetic field generator that generates a first changing magnetic flux in a first flux region. A plurality of coupling loops have a first plurality of coupling loop portions spaced at a first wavelength along a measuring axis and a second plurality of coupling loop portions spaced at a second wavelength along a measuring axis. The 268 application further discloses that a third plurality of coupling loop portions is inductively coupled to a first changing magnetic flux from a transmitter winding in a first flux region to generate second and third changing magnetic fluxes outside the first flux region in the first plurality of coupling loop portions and the second plurality of coupling loop portions, respectively. The second and third changing magnetic fluxes inductively couples those coupling loop portions to first and second pluralities of receiver windings, respectively.
A capacitive incremental position transducer system is disclosed in U.S. Pat. No. 5,886,519 to Masreliez et al., incorporated herein by reference in its entirety. In this capacitive incremental position transducer system, the system has two members movable relative to each other and includes a fine track transducer. The fine track transducer is associated with a particular wavelength. The design of this capactive incremental transducer could be replicated at a second, different, wavelength along a second track on the same transducer substrate, and the phase difference between the outputs of the two capactive tracks could be used to establish an absolute position, in a manner analogous to the higher-level signal processing methods disclosed in the previously mentioned inductive transducer patents.
Increasing the absolute measurement range of inductive andcapacitive transducers is desirable for a variety of reasons. However, the absolute range is limited in known transducers. Specifically, with currently known inductive or capacitive transducers, it is difficult to increase the absolute measurement range while simultaneously maintaining a high resolution and small number of tracks (each track is associated with a particular spatial wavelength). Rather, to increase absolute measurement range using known techniques, it is necessary to increase the number of tracks in the position transducer and/or to reduce the resolution of the finest track. An increased number of tracks results in increased fabrication costs, as well as increased complexity and size of the transducer.
This problem occurs because the absolute range of a transducer is inversely proportional to the difference xcex1xe2x88x92xcex2 between the spatial wavelengths xcex1 and xcex2 of the two tracks in a transducer. Additionally, the resolution is proportional to the finest wavelength, i.e., proportional to the smaller of xcex1 and xcex2. Consequently, to increase the absolute measurement range while keeping the resolution fixed, the difference between the wavelengths of the two tracks, i.e., xcex1xe2x88x92xcex2, is reduced. However, due to inherent transducer errors, this difference will rapidly become impracticably small and difficult to reliably measure, thus resulting in a poor transducer accuracy. To further increase the absolute range while maintaining high accuracy and resolution, a third track, with a wavelength xcex3, must be used. The use of such a third track is described in the incorporated 274 patent. However, this third track adds additional cost, complexity and size, as described above.
Accordingly, this invention provides systems and methods for increasing the absolute measurement range that an absolute position transducer is capable of measuring.
This invention separately provides systems and methods that eliminate the need for a third track and, in some cases, the second track in an absolute position transducer.
This invention separately provides an absolute position transducer that has a substantially simplified design.
This invention separately provides an absolute position transducer that has lower manufacturing cost.
This invention separately provides an absolute position transducer that provides the ability to utilize a narrower scale.
This invention separately provides an absolute position transducer that allows for the reduction of the wavelength associated with each track, thus improving the resolution of the position transducer.
This invention separately provides an absolute position transducer that may be used with relatively simplified electronics. Illustratively, in some cases, the absolute position transducer may be used with three or fewer electronic channels.
This invention separately provides an absolute position transducer that is suitable for a wide variety of applications.
In accordance with the systems and methods of this invention, one exemplary embodiment of the absolute position transducer uses two members moveable relative to each other along a measuring axis of the position transducer. A first member contains at least one transmitter winding that each generates a changing magnetic field and at least two sets of receiver windings that sense proximate magnetic fields. The two or more sets of receiver windings have similar, but different, wavelengths. Thus, the spatial phase difference between the two wavelengths at a given position defines a coarse wavelength much longer than either of the individual wavelengths.
The second member has at least two sets of flux modulating elements, such as flux modulators or flux coupling loops, regularly positioned along the support member, at first and second predetermined intervals (wavelengths) corresponding to the wavelengths of the two sets of receiver windings. Each set of flux modulators or flux coupling loops is positionable within the magnetic flux generated by a corresponding one of the transmitter windings. The flux modulators can be either flux disrupters or flux enhancers. The flux modulating elements modulate the magnetic field inductive coupling proximate to the receiver windings, depending on the relative position between the first and second members.
As a result, a spatial dependence is introduced into the output of the position transducer. The spatial dependence is dependent upon the relative positioning of the first member and the second member. An electronic circuit coupled to the transmitter windings and the sets of receiver windings evaluates and compares the two outputs of the sets of receiver windings, evaluates the absolute position between the two members, and exhibits the position on a display.
The properties or characteristics of the flux modulating elements vary uniquely along the measuring axis over a range that is longer than any other wavelength of the transducer, including the coarse wavelength. In one exemplary embodiment, the variation is treated as a third wavelength that is at least as long as the extent of the flux modulating elements on the second member. As a result, the degree of flux modulation generated by the flux modulating elements of the second member will vary along the measuring axis of the absolute position transducer. An additional spatial dependence is thus introduced into the position transducer. This spatial dependence appears in the amplitude of the signals output by the pairs of receiver windings in each set of windings.
These and other features and advantages of this invention are described in or are apparent from the following detailed description of the preferred embodiments.